The present invention relates to steam separators and the like, such as are used in certain geothermal steam energy tapping applications. Horizontal separators for separating impurities from high pressure steam sources have been previously contemplated. Such horizontal separators include drain legs for accumulation of the impurities. In the known constructions, a portion of the steam along with the impurities is continuously supplied to the drain leg so as to keep the drain legs hot so that the material accumulated does not harden so hard that it cannot later be blown out at intermittent intervals. This steam supplied to the drain legs has previously been vented directly to the atmosphere, in order to assure the continuous flow into the drain legs which also aids in the continuous operational flow of the steam through the separator.
A difficulty with the previously contemplated arrangements mentioned above is that the steam supplied to the drain legs and vented directly to atmosphere has some adverse environmental impacts due to the impurities, heat, moisture, and noise associated therewith. In certain installations, the geothermal steam contains boron compounds and/or H.sub.2 S gas, which when vented to the surrounding atmosphere causes a bad odor and also precipitates out into unsightly deposits. Accordingly, it would be advantageous from an environmental standpoint to provide some method to control such vented steam, such as providing a system for collecting, recompressing, and pumping into the ground such vented steam. However such a system would be particularly expensive and require a lot of piping and other hardware. Furthermore, both the provisions for venting steam, and any provisions one may provide for preventing the vented steam from passing directly to the atmosphere, necessarily impair the overall throughput efficiency of the system.
Other separators have been contemplated which include a spinner section or static vane structure section which imparts centrifugal motion to the fluid with the outwardly centrifuged portion of the flow, containing the most impurities, being recycled back into the spinner section. This recycled flow travels adjacent a sump or drain leg to accommodate gravity separation of the impurities and liquids, prior to being reintroduced back into the spinner section. Since a large part, on the order of 10% total flow, is recycled the throughflow efficiency of such separators is limited. In such a system, if the steam flow is not intentionally cycled into the drip leg, the temperature of the drip leg may not be reliably maintained by the steam so as to prevent hardening of the solid impurities. On the other hand, the liquid or water which would fall into the drip leg may partially accommodate the maintenance of the temperature of the solids. However, this water would create the need for some type of drain or other system to remove the liquid.
The present invention contemplates an arrangement which will overcome the drawbacks of the above-noted prior art arrangements at a minimum of constructional expenditures. According to particularly preferred embodiments of the present invention, it is proposed to provide a separator with steam continuously supplied to the drain or drip legs to maintain the temperature thereof and then to have a low pressure region at the upstream end of the separator to accommodate recycling of the steam from the drain legs back into the separator.
According to particularly preferred embodiments of the invention, the separator is provided with an ejector type of pump. This type of combination of separator and ejector pump utilizes the energy in the incoming steam supply to facilitate the recycle pumping action of the steam from the drain leg connections. It is contemplated that recycling of 1/2% to 11/2% of the total steam flow will accommodate the heating of the drip legs and optimize the total efficiency of the separator.
Particularly preferred embodiments utilize separators having a first so-called "knock-out" section and a downstream spinner or centrifuging section. The knock-out section serves to deflect the large solid particles coming in from the raw supply of geothermal steam, and prevents these from being ingested into the system spinner section to plug the same up or the like. A separate drip leg is then provided for each of the knock-out section and the spinner section to collect the solids separated. In these systems having multiple drain legs, the present invention contemplates controlling the recycle conduits so that they have substantially equal flow rates back into the ejector pump.
Preferred embodiments of the present invention also contemplate inclusion of flow reversing mechanisms, such as conical inlet members, in the drain legs themselves so as to assure a reversal of the steam flow within the drain leg with consequent improved removal of impurities from the steam before it is recycled back into the separator inlet. The reversal of the drain leg steam flow portion is assured by placing the connections for the conduits leading back to the inlet at a position disposed vertically above the bottom of the conical inlet openings of the conical inserts in the drain legs.
The apparatus and method of the preferred embodiments of the present invention exhibit many advantages including:
(i) venting of steam to atmosphere is avoided while obtaining the use of the hot steam to heat the drain legs and prevent hardening of the solid impurities collecting in the drain legs;
(ii) the overall efficiency of the system is optimized by controlling the amount of drain legs steam to be recycled to optimize the needs of the systems;
(iii) the maintenance required is minimized since only static structure is required, once the system has been set up, an advantage that is particularly important in practical applications where geothermal wells are at remote locations that can't be economically continuously monitored;
(iv) the manufacturing expenditures are minimized due to the simplified constructions;
(v) the system can be retrofitted to many existing systems which now continuously vent the drain leg steam to atmosphere;
(vi) in embodiments with multiple drain legs, the flow back into the ejector pump at the separator inlet is balanced and symmetrically supplied about the circumference of the inlet so that the ejector pump operates efficiently and reliably.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.